As the processing speed and memory capacity of computers have continued to increase, along with advances in computer graphics software, the interest in imaging both the geometry and surface texture of three-dimensional ("3D") objects has also increased. Numerous applications of such technology which for many years were anticipated have begun to be realized. The use of 3D representations has expanded in many areas, including entertainment, animation, industrial design, engineering, archiving, commercial advertising, catalogs, and "virtual reality" visits to actual places (e.g., cities and museums).
Various techniques have in turn developed to capture this information. Some are mechanical, some are purely based on images. Each system proposes different tradeoffs. The main parameters to be considered include: cost, accuracy, ease of use, and speed of acquisition. So far most commercial 3D scanners have favored accuracy over other parameters. However, while accurate, these systems tend to be very expensive.
One example of a mechanical system uses physical contact with the object to measure its surface. A robot arm "feels" the object and records the variations in dimension. The object may be rotated or otherwise adjusted to allow for multiple measurements. This type of system is typically expensive, bulky and slow.
Another group of systems uses active lighting, such as a laser or LCD projector. Typically these systems also use motorized transport of the object. The object is lit by projected light and rotated to provide views from multiple angles. While such systems are very accurate, they are also typically very expensive and bulky. Another disadvantage of lasers is that they are potentially dangerous to the operator's eyes, reducing the applicability of these systems to consumer use.
Some computer vision researchers have considered taking a different approach, favoring cost and ease of use while sacrificing some accuracy and speed. A number of ways of obtaining information on 3D shapes from more passively acquired images have long been known: stereoscopic disparity, texture, motion parallax, (de)focus, shading and specularities, occluding contours and other surface discontinuities. Unfortunately, the single passive cue that gives reasonable accuracy, stereoscopic disparity, has two major drawbacks: (a) it requires two cameras, and (b) it is typically ineffective on untextured surfaces. Accordingly, such a system is not inexpensive because of multiple cameras. In addition, because the great majority of industrially manufactured objects do not have textured surfaces, stereoscopic disparity is not suitable for a large number of applications.
The inventors have determined that a better technique for representation is found using shadow rather than lasers or multiple cameras. Accordingly they have developed the methods and apparatus for capturing 3D surfaces based on structured lighting described in the present disclosure.